1. Field of the Invention
The present invention relates to a display device that has a display surface and which can display information such as an image, a character and the like on the display surface, and particularly to a display device configured to be able to detect an object to be detected in contact with or in proximity to a display surface.
2. Description of the Related Art
Liquid crystal display devices, organic EL (Electro Luminescence) display devices, and display devices using electrophoresis are known as display devices capable of displaying information such as an image, a character and the like.
With decreases in thickness of the display devices, the display devices are desired to become multifunctional combining an original function of displaying video and text information and the like and a function of an input device or the like to which a user designation or the like is input. A display device detecting that a finger of a user or a stylus pen (so-called touch pen or the like) has come into contact with or into proximity to a display surface is known as a display device that meets this desire.
Contact detection can be performed by a resistive film type or a capacitance type touch panel. A display device having a touch panel added to the display surface side of a display panel such as a liquid crystal panel or the like is known.
However, the addition of the touch panel is disadvantageous for reduction in thickness of the display panel, and is a factor in increasing cost. The resistive film type touch panel, in particular, cannot detect a change in resistance value unless a screen is pushed with a certain degree of force, so that a display surface is distorted. In addition, the resistive film type touch panel performs one-point detection in principle, and thus has limited uses.
A display device having an optical position detecting function by including a light receiving element for indicated position detection in a display panel is known as an indicated position detecting system that does not require a touch panel (see Japanese Patent Laid-Open No. 2005-275644 and Japanese Patent Laid-Open No. 2006-301864, hereinafter referred to as Patent Documents 1 and 2 respectively).
A system that detects the shadow of extraneous light by a light receiving element is widely used in optical position detection.
On the other hand, a display device described in Patent Document 2 includes a light receiving element (hereinafter referred to as a light sensor) having sensitivity to non-visible light within a liquid crystal (or an organic EL) display panel. In the case of the liquid crystal display panel, a backlight is disposed on one principal plane (rear) side of the liquid crystal display panel. Light from the backlight includes a visible light component and a non-visible light component. The light from the backlight undergoes modulation according to an input video signal in a liquid crystal layer when passing through the liquid crystal display panel, and is then emitted from another principal plane (a front or a display surface). A predetermined image is displayed by modulating the visible light component of the emitted light (outgoing light).
When there is an object (that is a finger of a human, a stylus pen, or the like, and which will hereinafter be referred to as an object to be detected) in contact with or in proximity to the display surface side of the liquid crystal display panel, a part of the emitted light is reflected by the object to be detected, and is then guided as reflected light to the side of the light sensor. The light sensor detects a non-visible light component, in particular, of the reflected light from the object to be detected. A visible light blocking (non-visible light selecting) filter is provided so as to correspond to a region where the light sensor is disposed, and the transmitted light does not undergo modulation according to a video signal in the region. Therefore the detection of the object to be detected can be performed without affecting a display state and without being affected by a degree of brightness of surroundings. The position and size of the object to be detected can be detected by arranging a large number of light sensors regularly (discretely and two-dimensionally).
The organic EL display device does not need a backlight. Pixels themselves emit light in the organic EL display device. In this case, non-visible light emitting elements and light receiving elements are arranged at predetermined intervals within the display region of a panel. A method itself of detecting an object to be detected is similar to that of the above-described liquid crystal display device. Non-visible light from the light emitting elements is reflected by the object to be detected. By detecting difference between amounts of reflected light at this time by the plurality of light receiving elements arranged discretely and two-dimensionally, the position and size of the object to be detected can be detected.
A display device described in Patent Document 1 includes a light sensor on the backlight side of a spacer separating a liquid crystal layer for each pixel. A region within a pixel which region is different from the region where the light sensor is disposed includes a region configured to dispose a light receiving element (hereinafter referred to as a visible light sensor) having sensitivity to visible light and a region that can change voltage applied to the liquid crystal layer and thus modulate transmitted light according to a video signal (which region will hereinafter be referred to as a light modulating region).
The display device described in Patent Document 1 is configured to be able to detect both the visible light component and the non-visible light component of light reflected by an object to be detected such as a finger of a human, a stylus pen or the like.
According to the techniques described in Patent Documents 1 and 2, object detection is performed using non-visible light, which is invisible to the human eye and thus does not affect displayed video. Thus, in a case where an amount of transmitted light of visible light which transmitted light passes from a rear side to a front side is substantially close to zero as in black screen display, display is not affected even when non-visible light is passed to the front side. Therefore an object to be detected can be detected even at a time of black display. The object can be detected regardless of whether surroundings are dark or bright.
[Non-Patent Document 1]
S. Klein et al. Journal of Applied Physics 98, 24905, (2005)
[Non-Patent Document 2]
K. H. Jun et al. Physical Review B 66, 15301, (2002)